1. Field of the Invention
The present invention relates to a logic circuit and a semiconductor device including the logic circuit. Further, the present invention relates to an electronic device including the semiconductor device.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electro-optical device, a light-emitting display device, a large scale integrated circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
In general, a circuit configuration of a semiconductor integrated circuit typified by a large scale integration (LSI) circuit is fixed at the time of manufacture and cannot be changed after the manufacture. In contrast, a semiconductor integrated circuit called a programmable logic device (PLD) has a structure in which unit logic blocks each including a plurality of logic circuits are electrically connected to each other through wirings. In the programmable logic device, a circuit configuration of each logic block can be controlled by an electric signal.
Accordingly, the design of the programmable logic device can be changed even after the manufacture. Thus, time and cost required for designing and developing a semiconductor integrated circuit can be greatly reduced with the use of the programmable logic device.
Programmable logic devices include a complex PLD (CPLD) and a field programmable gate array (FPGA). In either of the programmable logic devices, a circuit configuration of each logic block is controlled by a programmable switch in the logic block, which performs switching in accordance with data (configuration data) stored in a memory portion. In other words, data is programmed into each programmable switch, whereby a circuit configuration of a programmable logic device can be changed.
A volatile memory such as a static random access memory (SRAM) is mainly used in the above-described memory portion. On the other hand, as disclosed in Patent Document 1, a non-volatile memory including a floating gate transistor, such as a flash memory, is included in the memory portion in some cases (see Patent Document 1).